AD7782(Rev0) Просмотр технического описания (PDF) - Analog Devices
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AD7782 Datasheet PDF : 12 Pages
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Typical Performance Characteristics
9
8
7
6
5
4
3
2
1
0
TPC 1. Noise Distribution Histogram
AD7782
3.0
2.5
؎2.56V RANGE
2.0
VDD = 5V
1.5
VREF = 2.5V
TA = 25؇C
1.0
؎160mV RANGE
0.5
0
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
VREF – V
TPC 2. RMS Noise vs. Reference Input
ADC CIRCUIT INFORMATION
Overview
The AD7782 incorporates an analog multiplexer with a Σ-∆ ADC
channel, on-chip programmable gain amplifier, and on-chip digital
filtering intended for the measurement of wide dynamic range,
low-frequency signals such as those in weigh-scale, strain-gage,
pressure transducer, or temperature measurement applications.
This ADC input is buffered and can be programmed to have an
input voltage range of ± 160 mV or ± 2.56 V. The input channels
are configured as two fully differential inputs. Buffering the input
channels means that the part can accommodate significant source
impedances on the analog inputs and that R, C filtering (for
noise rejection or RFI reduction) can be placed on the analog
inputs if required. The device requires an external reference of
+2.5 V nominal. Figure 3 shows the basic connections required
to operate the part.
POWER
SUPPLY
10F
0.1F
IN+
OUT–
IN–
OUT+
10k⍀
6k⍀
VDD
AD7782
AIN1(+)
CS
AIN1(–)
DOUT/RDY
AIN2(+)
AIN2(–)
SCLK
REFIN(+)
REFIN(–)
XTAL1
XTAL2
GND
CONTROLLER
32.768kHz
CRYSTAL
Figure 3. Basic Connection Diagram
The output rate of the AD7782 (fADC) equals:
fADC = 32.768 × 103 / (69 × 8 × 3)
while the settling time equals:
tSETTLE
=
2
fADC
=
2 × tADC
Normal-mode rejection is the major function of the digital filter on
the AD7782. Simultaneous 50 Hz and 60 Hz rejection of better
than 60 dB is achieved as notches are placed at both 50 Hz and
60 Hz. Figure 4 shows the filter rejection.
0
–20
–40
–60
–80
–100
–120
–140
–160
0 10 20 30 40 50 60 70 80 90 100
FREQUENCY – Hz
OUTPUT DATA RATE = 19.8Hz
INPUT BANDWIDTH = 4.74Hz
50Hz REJECTION = –66dB, 50Hz ؎1Hz REJECTION = –60dB
60Hz REJECTION = –117dB, 60Hz ؎1Hz REJECTION = –94dB
Figure 4. Filter Profile (Filter Notches at
Both 50 Hz and 60 Hz)
REV. 0
–7–
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